The processing of beverages, such as beer, ale, wine and fruit juices, require clarification steps which involve passing the beverage through filter media. Beds of loose diatomaceous earth and perlite are often used. Filter sheets incorporating diatomaceous earth or perlite with sheet-forming fibers, such as cellulose, are also commonly used. These filter media contain small amounts of various minerals and compounds, among which are iron compounds. A certain portion of the iron content of the filter media is soluble in the beverages which are treated. The portion of the iron which is soluble is referred to in the beverage industry as "beverage soluble iron" (often abbreviated "BSI"). The presence of high levels of BSI dissolved in the beverages is deleterious to the taste and long term stability of the beverages. Consequently, it is desirable to have a filter media which is low in BSI content and which retains desirable filtration and clarification properties.
There are various known processes for reducing the BSI content of filter media, particularly diatomaceous earth or diatomite. For example, U.S. Pat. No. 4,134,857 to Bradley discloses a low beverage soluble iron content filteraid, especially diatomite, which is produced by a method which comprises contacting a granular filteraid with tannic acid, gallic acid or mixtures thereof, preferably in aqueous solution. Also discussed in the Bradley patent is an attempt to use other contacting fluids to determine if there were other materials equivalent to tannic and gallic acids. In particular, water, starch, sucrose, monobasic sodium phosphate, tartaric acid, gluconic acid, salicylic acid, and the sodium salt of ethylene diamine tetra acetic acid were all tried. It is indicated that the organic acids tried in this group produced only insignificant reduction in BSI. It is also indicated that the remaining materials are able to reduce the BSI by larger amounts than the organic acids, but require longer time periods (often ten days to two weeks) to reach the BSI reduction levels obtained with tannic and gallic acid in a matter of minutes.
U.S. Pat. No. 4,187,174 to Nielsen et al. describes a method for treating diatomaceous earth filteraids having a beer soluble iron content of less than about 0.01 percent to further reduce the beer soluble iron content. In the method, the filteraids are maintained in contact with a relatively small volume of an aqueous solution of an acid. The acid solution is added to the diatomaceous earth filteraids at a level of less than about 15 percent by weight, based on the weight of the dry filteraids, which is sufficient, but not in excess to wet the filteraid uniformly. After a period of time, it is indicated that the beer-soluble iron content of the filteraid is reduced by about 30 percent.
Various other acid treatment processes for reducing the beverage soluble iron content of diatomaceous earth are known, such as are described in U.S. Pat. No. 665,652 to Enzinger, U.S. Pat. No. 2,701,240 to Bregar and U.S. Pat. No. 1,992,647 to Schuetz. The prior art methods, however, fail to reduce the beverage soluble content in filteraids to the extremely low levels particularly required in the brewing industry. Further, the known methods involve a lengthy time period for processing or require a complicated or expensive procedure.
Accordingly, it is a primary object of the present invention to reduce beverage soluble iron in filteraids to an extremely low level.
It is a further object to reduce the beverage soluble iron in diatomaceous earth filteraids by a method employing particular chelating agents.